Travelling in a car as a family. Help!!!

Hi, I would love some advice. My son is 14years old and he is autistic. We also have a 5 year old and a 7 year old. If we are ever in the car altogether there is an argument within seconds. Harry gets annoyed if they touch him by accident or sing along to the music in the car or sometimes if they even talk. What skills can we learn to help in this situation. Thank you for any advice you can give us. We need help!!!